Stabilization of vinyl pyridines



2,857,389 STABILIZATION OF VINYL PYRIDINES Anton M. Schnitzer, Dewey,and Robert E. Reusser, Bartlesville, Okla., assignors to PhillipsPetroleum Company, a corporation of Delaware No Drawing. ApplicationJuly 5, 1955 Serial No. 520,117

'11 Claims. Cl. 260-290 This invention relates to the stabilization ofvinyl-substituted heterocyclic compounds having a heteronitrogen atom.In another aspect of the invention, it relates to the stabilization ofvinylpyridine compounds.

In the manufacture of vinylpyridines and other vinylsubstitutedheterocyclic nitrogen compounds, one of the principal difi'icultiesencountered is the tendency for these vinyl compounds to polymerize atambient temperatures. This tendency is especially pronounced when theyare subjected to elevated temperatures. These vinyl compounds are-usedas monomers in polymerization reactions, and the presence of solubleand/or insoluble polymers in the vinylpyridine monomers u'se'for thispurpose. The problem reaches its peak when such vinyl compounds areprocessed in the presence. of heat, for example, in the distillation ofthese compounds. Polymers are also formed at ambient temperatures whenthe vinylpyridine compounds are'stored and transported.-

provide an effective the formation of both It becomes important,therefore, to stabilizing agent which will inhibit soluble and insolublepolymers monomers.

Vinylpyridine can be prepared by the dehydrogenation of. a correspondingalkylpyridine by a method disclosed in the copending application244,469, filed August 30, 1951, now Patent No. 2,769,811, for ThePreparation of 2-Methyl-5-Vinylpyridine from 2-Methyl-5-'Ethylpyridine.- The efiluent from this dehydrogenationreaction is separated in a-combined steam and vacuumfractionaldistillation, and this separation has beenfound to be very difficulh notonly due to the proximity of the boiling points of the major components,but also due to the tendency of the Z-methyl-S-vinylpyridine topolymerize. -The efiiuent is subjected'to heat'in the range of 180 to220F. during this steam and vacuum distillation, and operation of thisdistillation step can bein the vinylpyridine come extremely difiicultbecause of the formation of polymers unless a suitable stabilizing agentis used. The following are objects of the invention. 7

It is an object of this invention to provide a method for inhibiting the1 eterocyclic nitrogen atom.

Another object of the invention is to provide a method for inhibitingthe formation of both soluble and insoluble polymers invinyl-substituted heterocyclic compounds havpolymerization ofvinyl-substituted compounds having a hetero nitrogen ing a heteronitrogen atom.

A further object of the invention is to provide a method for preventingpolymerization ditions of fractional distillation.

Other and further objects of the invention will become apparent to thoseskilled in the art upon consideration of the following disclosure.

We have discovered that the aforementioned objects are attained byadding to vinyl-substituted heterocyclic compounds having a heteronitrogen atom a polymerization inhibiting amount of at least one ofcertain phen-oxazine compounds. The phenoxazine compounds, and mixturescan prevent their of John E. Mahan, Serial No.

of vinylpyridine-under con and iodineyan "with an amino group ordi-'s1ibstitut'ed.iwth-'alkyl groups containing up to 5- hydrogenradical where R is as indicated hereinabove.

thereof, which are effectiverinhibitors in accordance with thisinvention include those represented by the following structuralformulas:

With reference t-o the above listed formulas, R can be hydrogen, ahydroxyl group, an -'-ONH radical, a sulfonic acid group, a carboxylgroup, an alkyl ester of a carboxyl group containing up to 6 carbonatoms, a halogen selected from the group consisting of chlorine, bromineis an amino group or an amide group, substituted group or it may' bemono- With an alkyl group containing up to 5 with a phenyl group whichitself may be it may be an urior di-substituted carbon atoms ormono-substituted which latter group may be monocarbon atoms. --R mayalso'be present'in the halide salt form of any of the aforementionedamino groups. At least one of the Rs is either a hydroxyl group or anamino group as described above, and furthermore at least three of the Rsare hydrogen. X can be a halogen selected from the group consisting ofchlorine, bromine, and iodine or an acid sulfate group.Additionally,'any two adjacent Rs, R s, on at least one of rings I andcanbea II of the above formulas tat-(i=0 In this regard, it is notedthat the nucleus of the polycyclic radical formed by the addition of theR R R R B radicalwill not contain more than 10 carbon atoms.

The phenoxazine compounds to which this invention re.- lates can also bedefined as being selected from the group consisting of phenoxazineshaving structural formulas as Patented:,-Oct. 21, 1958- amino group, oran amide group. If R and only two adjacent indicated above'w-herethe--11-r-a'dical is selected from the -COOH, an alkyl ester of COOHcontaining up to 6 carbon atoms, Cl, -Br, --I,

hydrogen halide salts of and -o oN i where R is selected" from t hegroup consisting of and where R is selected from the-group consisting of-H, -C,,H when n is an integer tro'm l to 5, inclusive,

where R is selected'from the group consisting of H,

and hydrogen halide salts of and where two adjacent R radicals, and onlytwo adjacent -R radicals, on at least one of rings I and II .can bewhere R is as indicated'aborfe; atleajstone'Rf radical be ing selectedfrom the group, consistingof-" ol-fand and at least 3 Rradicals:beingie-vi-lpand iwhere "X is lected from the group consisting .of Cl-Br, -I;- and Specific workings examples of iphenoxazi'ne compoundswhich can be used -as inhibitors in-accordance' with'this systemfollowed the group consisting of hydro en;

4 i 223, published by The Interscience Encyclopedia, Inc., New York(1948-); in Farbstofltabellen von Gustav Schultz, siebente Auflage, neubearbeitet and erweitert von Dr. Ludwig Lehmann, Leipzig, AkademischeVerlagsgesellschaft m. b. H. (1931), lithographed by Edwards Brothers,Inc., Ann Arbor, Michigan (1945); and in Bellsteins Handbuch derOrganischen Chemie, vierte Aufiage.

As has been indicated above, the pheno gazine compounds of thisinvention are effective to inhibit the formation of bothsoluble andinsoluble polymers in vinyl-sub stituted heterocyclic compoundshavin'g ahetero nitrogen atom. The insoluble polymer is also commonly known aspopcorn polymer and isan insoluble, hard, porous and opaque material.Popcorn polymer is aptly named because it resembles popcorn inappearance.

We wish to point" out that we' intend that the terms stabilizer,inhibitor or inhibiting agent, used herein, shall have essentially thesame meaning, and that they areused-f re senti'anyjthe same' itrpbfse,ch igh'a't'e'thesubstances'disclosed'hereiti whic p vent merization ofthe vinyl-substituted hefterocy'c c manger compounds. Itisn'o't'interidedithattliese terms necessarily shall'denote amechanismbywhich this s'tabili'zing'action is'accornplished; I

One group of polymeriz'able'" vinyl-substituted heterocycli'cc'om'poundscontaining a'hete'ro'nitrogenatomwhicli canbestabilize'd in accordancewith ourinvention is the monoand dlvinylpyridiiies',with'the'vi'riylradical being resent in" any of the several positionsiii the yridine nucleus; Alkyl'radicals can be present on the rig,o'r'oii' the alpha carbon atom of thevinyl' radical, but the fiambierofcarbon-momma the combined-alkyl radicals should enerally'n'ot liereaterthan lz; These alkyl radicals are preferably methyl and ethylradicals. tabh'ed ib'eiiibbfti" a'toifi'sfi'n v alkyl,vinyland'isopropenyl (alpha methylvinyl) radicals; at least one,- andnot mor'e'thantwo, 'ofs'aid radicals being vinyl or alphanietliylvinylwith the total number of 'cai'boh atoms in the alkyl radicals being notgreaterthan 12. Examples of such compounds are Z-vinylpyrIdi'ne, 3-vinylpyridine, 4+ vinylpyridine, 2,5-divinylpyridine, Z-methYI S vinyI jridine, 2 -vinyl- 5-ethylpyridine,- 2,BQ4-trifiiethyl-S-vinylpyridine,3,4,5, -tetramethyl-Zvinylpyridine, 3-e th yl--vinyl:

Qther polymerizableheterocyclieeompounds contain line;8+ethyl-2-vinylquinoline, 4-hexyl-5-vinylquinoline,j l

vinylifsoquinoline; 5 methyl-l-isoprop.enylisoquinoline, -l 8divinylisoquinoline, vinylpyrrolidone, vinylpyrrole, vmylpiperidineand-vinylpyrrolidine, and the like Normally,

the; vinyl substituent will'be. attached to aring carbon atom. However,in compounds wherein the-ring nitrogen atom ,is a secondary nitrogenatom, the-vinylgroup-can instead'be attachedv to this-ringjnitrogen-atom, for example, N-vinylcarbazole andN-vinylpyrrolidone.-' The process of this invention :-is particularlyapplicable to organic or hydrocarbon mixtures containingsubstantialproportions ofa vinylpyridine compound, i. e., that amountwhich causesdifficulties due to its polymerizatiom- -e. gz, over 5.0 percent.Examples of vinylpyridine compounds subs'titherits' at the ring canbelsele'ctedi notacontained in such mixtures are 2-vinyl-4,6-dimethylpyridine,- 2-methyl-4-vinylpyridine,Z-methyl-S-vinylpyridine, 5-ethyl-2-vinylpyridine, and5-amyl-2-vinylpyridine.

In carrying out the invention, solution of the stabilizing agent in thevinylpyridine, or other heterocyclic compound containing a heteronitrogen atom to be stabilized, can be accomplished in any suitablemanner, such as by agitating or stirring themixture containing thestabilizing agent, or merely by allowing the mixture to stand.Ultimately, the decision as to what concentration of the stabilizingagent to use will depend on variable factors, such as the temperatureand duration of time at a given temperature at which the heterocycliccompound containing a hetero nitrogen atom will be maintained wheninhibi tion of polymer formation is desired, and economicconsiderations. In the practice of this invention, a range ofconcentration from about 0.01 percent to 5.0 percent, or more, by weightof the phenoxazine compounds disclosed herein will be employed,preferably from 0.1 percent to 1.0 percent, all percentages being basedon the weight of the heterocyclic compound containing allete'ro nitrogenatom to be stabilized. Furthermore, the amount will depend on whichparticular heterocyclic containing a hetero nitrogen atom is concerned.

A more comprehensiveunderstanding of the invention may be obtained byreference to the following illustrative examples, which are, notintended, however, to be unduly limitative of the invention.

EXAMPLE I hibitor to be tested. The pieces of steel were added to I thevials in order to simulate steel vessels. The vials were then flushedwith nitrogen and sealed tightly with screw-on tops. The vials were thenplaced in an oven and maintained at 185 F. for 16 hours, after which aweighed sample of the contents of eachvial was evaporated under vacuumand over boiling water. The residue remaining, with allowance for theweight of inhrbitor present, was considered to be soluble polymer. Theresults of these tests are given below m Table I.

Table l i f Weight per- Amtilfililt 0t of1 Solul lto Inh tor e o ymerIuh b r (Weight (Average of percent) Several if 1. Mixture of'Aminophenoxaxon. and oxy-- Phemxazim Y 0.6 .65 Dimethylaminophenonahtha zoxonium chloride (Meldola Bluel 0. 60 0. 96Dimethylamino-oxy-diphenoxazoncarbonio acid (Gallocyanln) 0. 60 1. 09Control. 0. 0 25. 00

1 Prepared-by the oxidation of o-aminophenol as described in BeilstelnXIII, page 355. g

The structural formulas of thecompounds tested are as 1 follows: i t

(1) Aminophenoxazon compound 7 6 (2) Oxyphenoxyazim it I a (3)Dimethylaminophenonapthazoxoniumchloride (Meldola Blue) i H-d The datain Table I indicate that the phenoxazine compounds are very etfective inpreventing the formation of soluble polymer in a vinyl-substitutedheterocyclic nitrogen compound. The results are noteworthy because ofthe elevated temperature to which posed and also because of the verysmall amount of polymer which was formed under these conditions. Thecontrol was simply a sample of 2-methyl-5-vinylpyridine which wastreated in the way described for the other tests except that noinhibitor was added.

7 EXAMPLE II The phenoxazine compounds were also tested for theireffectiveness as inhibitors of soluble polymer formation by" thefollowing method. vinylpyridine containing amount of inhibitors to hoursat 185 pressure was adjusted to keep the temperature of the distillationat 185 F., and this pressure was calculated to be approximately 250 mm.of mercury. After distillation, the samples were evaporated under vacuumover boiling water. The residue, with allowance for weight of inhibitorpresent, was considered to be soluble polymer. The results of thesetests are tabulated below in Table II. In these data, the percent ofinhibitor used is expressed as a weight percent of theZ-methyl-S-vinylpyridine.

Weighed samples of 2-methyl-5- 5 weight percent water and an be testedwere distilled for 16 Table II I Weight Amount of Percent of CompoundInhibitor Soluble (Weight Polymer percent) (Avg. of2

Phenoxazine 8:3 :3? Control 0 0 26.00

Mlxture of aminophenoxazon and oxyphenoxyazlm prepared by the oxidationof o-aminophenol as described in Beilstem XIII, pp. 355.

The data in Table II shows that phenoxazine com.

F. under conditions of total reflux. The

the samples were expounds are 'efiectivein distillation processes Where.the

7 need for the inhibitors is of the greatest commercial im= portance.The control was a sample of 2-me'thyl-5- vinylpyridine whichwassubjected to the same conditions as samples containing an inhibitorexcept that no inhibitor was used.

7 EXAMPLE In These phenoxazine compounds were further tested aspolymerization inhibitors to determine their effectiveness underconditions of storage and/or'transit of Z-methyl- -vinylpyridine. Inthese tests, the vials, eachcontaining a small piece of steel, werecharged with flashed 2-methyl- 5-viny1pyridine to which had been added0.1 weight percent of the inhibitor. The small pieces of steel wereadded to the vials in order to simulate steel vessels. Thirty-fivepercent of thev'olur'ne of each vial was left empty to provide an aircover for each sample and to thereby simulateconditions of storage andtransit. The vials were sealed with screw caps and maintained at 100 F.during the test period. The results of these tests are given below inTable III.

The. data in Table III show that-novsoluble. polymer was formed in the2-methyl-5-vinylpyridine under. the conditions of the test.

EXAMPLE IV Tests were: made in order to ascertain the efiectiveness ofphenoxazine compounds as. inhibitors for popcorn polymer formation. invZ-methyl-S-vinylpyridine. Samples of flashed Z-methyl-S-vinylpyridinewere-placed. in vials,. and to each sample there was added 0.3 weightpercent divinylbenzene and the stated amount of inhibitor. Thirty-livepercent. of the volume of. each. vial. was. left empty to provide. anair space. The control. wasprepared in. the. same way except that noinhibitor was. added. The vials were sealed with screw caps and. then.placed: in an-oven maintained at 185. E, and-the results of-thesetestsare noted below in Table IV.

Table IQV .Amount of Inhibitor-- Inhibitor! Used Results (Weightpercent) Phenoxazinek. 0:01 No popcorn'polyrner in 34'd'a'ys.Phenoxazinei t 051: Do;- p Control 0.0 100 percent popcorn polymer ineight hours.

I See footnote under Table II.

Thedata in Table IV indicate that the phenoxazine compoiindsare veryefiective in preventingthe formation of insoluble orpopcorn polymer evenwhen the sample of he. in lni bst tu d-h emw n tr e Y R F PP Q imaintained at elevated temperatures for extended periods of time. e i

EXAMPLE V Tests were made. to; determinei'ther eiiectivcness of: thephenoxazine compounds as inhibitors during the vac uumLdistillationi of2-methyl-5-vinylpyridine: (MVP) in a pilot plantcolumn which wascontrolled so as tov closely simulate commercial scale operationswherein the efiluent from the dehydrogenation of LmethyhS-ethylpyridineis subjected to a steam and vacuum distillation. In these tests a;column; was used which was 2 inches in'diameter and 4 feet high andpaeked With- A" stainless steelHelipack (No. 2918-). This column wasdesigned so that inhibitedg-water saturatedMV P would-befedinto the topofthe'colurnn at: a controlled rate of ml. per hour.

The column-kettle wascharged initially with 650- grams.

ot- MVP containing 5.0- weight percent water and inhibitor at the,desired concentration. The feed mixture was flashed MVP-1 with an added-15 weight percent of water and airinhibitor at a concentration ofone-tenthof that'tised-in the-ikettle The column wasoperatedso' that theamount of: distillate taken overhead was such that the inhibitor wasconcentrated by a; factor of 10 as it progressed: down thecolumng-resiilting a i constant concentration of. inhibitor beingmaintained inthe kettle. The'kettl'e temperature was heldat- F; at 225otmercury by controlling the amount: of water added tothecolumnk'e't'tle? sampies-weregtaken from the kettle after a'ten-hour'in't'er'v'a'l' and' analyzcdfor polymer by vacuum distillation overboiling water. The dataobtained using phenoxazine compounds-and sulfuras inhibitor's are g-ive'nhelow'in' Table V.

See tootnote under-Table II.-

The data} in Table? indicate that phenoxazine com pounds" are veryeffective in preventing polymerformation-inasteam and vacuumdistillation of a mixture of vinylp'yrid-ines such as is producedby thedehydrogenationof" 2-methyl 5-ethylpyridine' to produce 2'-m'ethyl-"5-vinylpyridin'e 7 When the" henoxaaine compounds" are? used asinhibitors in the distillation of the effluent from the dehydrogenationof 2-methyl-5' ethylpyridine to produce Z-methyl-S-vinylpyridine theinhibitors can be added to the feed to the distillation column, anypoint along the column or th'e, inhibitor can be added to the reflux ofthe: distillationcolumn. It will be found that in some cases, a smalleramount of the inhibitor is effective when the inhibitor is added to thetop of the column or to the column reflux.

It will be understood tli'attlie foregoing disclosure is' illustrativeof our inventionand that other embodiments within the scope oftheinvention will occur to those skilled in the am Those skilled in theart wiiiappreeiate: for instance, that for tliepurpose ofthis'invention; vinyl substitutedlieterocycliccompounds having aheteronitrogen atom fiirth'er'substititt'ed'with n n-interferingi greup's;

for example, halo-, nitro-, amino-, hydroxyl-, and car'- H boxyl are thesameas non suhstituted' vinyl heterocyolic compounds having a heteronitrogen atom.

We claim:

1. A composition of matter comprising a polymerizable vinyl-substitutedheterocyclic compound having a hetero nitrogen atom, saidcompoundbeingselected from the group consistingfof mbnovin'ylpyridin'e andalkylsubstituted monovinylpyridinewherein the-total carbon atoms inalkyl substituent's does not exceed 12, and a polymerization inhibiting;amount of at least one polyassasse a merization inhibitor selected from'the group of pheno irazines having the following structural formulas: (ni where R is selected from th OH, COOH, and

group consisting of H,

where R is selected from the group consisting of --H and -C,,H n beingan integer from 1 to 5, inclusive, and where two adjacent R radicals,and only two adjacent R radicals, on at least one of rings I and H canbe where R is as indicated above; at least one R radical being selectedfrom the group consisting of OH and atoms in the alkyl substituents doesnot exceed 12, and a polymerization inhibiting amount of2-amino-3H-isophenoxazin-3-one.

3. A composition of matter comprising a polymerizable vinyl-substitutedheterocyclic compound having a hetero nitrogen atom, said compound beingselected from the group consisting of monovinylpyridine, andalkylsubstituted monovinylpyridine wherein the totalcarbon atoms in thealkyl substituents does not exceed 12, and

substituted monovinylpyridine wherein the total carbon a 'poIymerizationinhibiting amount of 2-hydroxy-3H-iso' phenoxazim-S-imine.

4. A composition of matter comprising a polymerizable vinyl-substitutedheterocyclic compound having a hetero nitrogen atom, said compound beingselected from the group consisting of monovinylpyridine, andalkylsubstituted monovinylpyridine wherein the to tal carbon atoms inthe alkyl'substituents does not exceed 12, and a polymerizationinhibiting amount of a'mixture of 2- amino-3H-isophenoxazin-3-one and2-hydroxy-3H-isophenoxazin-3-imine.

5. A composition of matter according to claim 1 wherein saidpolymerization inhibitor is 1,2-benzo-7-dimethylaminophenoxazoniumchloride.

6. A composition of matter according to claim 1 wherein saidpolymerization inhibitor is dimethylaminohydroxydiphenoxazoncarboxylicacid. 7 V

7. A composition of matter according to claim 1 wherein saidpolymerization inhibitor is 1,2-benzo-3-amino7-diethylaminophenoxazonium sulfate.

8. A meth cyclic compound having a hetero nitrogen atom againstpolymerization said heterocyclic compound being selected from the groupconsisting of monovinylpyridine and alkyl-substituted monovinylpyridinewherein the total carbon atoms in alkyl substituents does not exceed 12,which comprises adding to said heterocyclic compound a polymerizationinhibiting amount of at least one polymerization inhibitor selected fromthe group consisting where R is selected from the --OH, COOH and groupconsisting of --H,

where R' is selected from the group consisting of H and C I-I n being aninteger from 1 to 5, inclusive, and where two adjacent R radicals, andonly od for stabilizing'a' vinyl-substituted hetero- '11 two adjacent Rradicals; onaticast one ofrings I and II can be being selected from thegroup 'consi'stiag 6f -'-OH and of said polymerization inhibi toi"INS-$110111 0.01 to weight percent, based onili weight of said fit'efdcyciic cornp fiii f t I2. A 'ndc t fiod f'f stabilizing aVinyl-substituted heterocyclic esfipbirifid haying-a Beers nitrogen atoagainstpolyfrieriz'atiofg 'said h'ii" y'cl'ic compound being s 'electdffoiii the .gr'dfip as sting of monovinylpyridine arid alkyI-'subt-1fit'e"d monoyifiylpyridine wherein the total carbon stairs in alkylsubstituents does not exceed 12, which compiises adding to saidheterocyc l ic com= pound a polyifiei'i'zatioii inhibiting amount of2-amino- 3H-isophenoxazin-3-one.

' azoncarboxylic acid.

13.- A method for stabilizing a vinyl-substituted hetero cycliccompoundhaving. a heteronitrogen atom against polymerization, saidheterocyclic compound being selected from the group consisting "jfmonovinylpyridin and alkyl-substituted monovinylpyridine wherein thetotal carbon atoms inalkyl substituent's does not exceed 12, whichcomprises adding to said heterocyclic compound a polymerizatior'i'inhibiting amount of 2-hydroxy-3H- isophenoxazin-3-imine.

14. A method for stabilizing a vinyl-substituted heterocyclic compoundhaving a hetero nitrogen atom against polymerization, said heterocycl'i'compound being se lected from the group consisting of mon'ovinylpyridincand alkyl-substituted monovinylpyridine wherein the total carbon atomsin 'alkyl s'ubstituents does not exceed 12,

which comprises adding to said hcterocyclic compound a polymerizationinhibiting amount of a mixture of 2- amino-3H-isophenoxazi'n-3-one and2-hydroxy-3H-isophenoxazin-B-imine.

15. A method according to claim 8 wherein said polymerization inhibitor"is 1,2-benz"6-7-dimethylaminophenoxozonium chloride.- I

16. A method according'to claim 8 wherein said polymerization inhibitoris dim'ethylar'ninohydroxydiphenox- 17. A method according to claim 8'wherein said polymerization inhibitor is1,2-benzo-7-amino-7-diethylaminophenoxazonium sulfate. 7

No references cited.

1. A COMPOSITION OF MATTER COMPRISING A POLYMERIZABLE VINYL-SUBSTITUTEDHETEROCYCLIC COMPOUND HAVING A HETERO NITROGEN ATOM, SAID COMPOUND BEINGSELECTED FROM THE GROUP CONSISTING OF MONOVINYLPYRIDINE ANDALKYLSUBSTITUTED MONOVINYLPYRIDINE WHEREIN THE TOTAL CARBON ATOMS INALKYL SUBSTITUENTS DOES NOT EXCEED 12, AND A POLYMERIZATION INHIBITINGAMOUNT OF AT LERAST ONE POLYMERIZATION INHIBITOR SELECTED FROM THE GROUPOF PHENOXAZINES HAVING THE FOLLOWING STRUCTURAL FORMULAS: